With apparatuses provided with such as a propeller fan type blower and an outdoor unit of an air-conditioner (hereinafter, an air conditioning outdoor unit), to minimize turbulence and variations of inflow air into the blower is indispensable in order to reduce aerodynamic noises.
To achieve reduction of aerodynamic noises, it is effective to reduce a relative speed of a blade and a gas by making the diameter of an impeller large and to reduce an absolute speed of the gas by securing a passing cross sectional area of the gas.
In order to reduce turbulence and variations of inflow air into the blower, it is ideal to suction a gas with a rotation axis being the center from a sufficiently wide space which is homogeneous in the circumferential direction. However, even if taking the air conditioning outdoor unit on which a propeller fan type blower is mounted for an example, it is common that the suction space outside the radial direction of the blade is constituted by a plurality of side faces, the cross-section perpendicular to the fan rotation axis is basically a rectangular, and the extent of the space is often such that the bell mouth cannot have the a sufficiently large size whose cross-section has the same configuration for all the circumference.
Because flow vectors on the bell mouth face vary, conventional blowers elaborate a plan such that by changing a radius of curvature at the tip of the bell mouth suction side, separation of air flow in the vicinity of the bell mouth is suppressed to hold down the increase in turbulent sounds.
(Refer to Patent Document 1, for example).